Plasma ion fluxes in the ASDEX edge plasma during neutral-beam-heated discharges

Abstract

Deuterium fluxes parallel to the toroidal magnetic field in the plasma boundary of the midplane of ASDEX were collected with graphite collector probes positioned at a distance of about 5 to 10 cm from the separatrix, and then quantitatively analysed by the nuclear reaction D(3He, p)4He. The time resolution of about 0.1 s of the measuring setup allows the fluxes to be collected during the ohmic heating plateau phase (about 1 s) of the ASDEX discharge (typically 2 to 3 s) and during the neutral injection phase (about 0.2 s). The measurements yield fluxes of 1016 to 1017 D/cm2 s in the plateau phase, and fluxes one order of magnitude larger during the neutral injection phase. In the ohmic heating phase the e-folding length of the curve described by the measured points is observed to be about 1.5 cm. During neutral injection in discharges of the H-type the e-folding length was found to be about 8 cm. A series of such measurements is presented and discussed, with particular regard to the plasma-wall behavior during L-type and H-type discharges.